The foot injury of running back Andre Ellington is one of the things the Cardinals have worked around during their 2-0 start.

In 1977, Muhammad Ali put his hands on the ropes during a nationally televised boxing exhibition and invited Michael Dokes' best shot. Ali bobbed and weaved for 10 seconds, dodging 21 punches in all, and then celebrated with a hip-swaying shimmy, as if the preternatural reflexes to avoid every unencumbered swing did not surprise him one bit.

Cardinals coach Bruce Arians does not move that fast, but he could feel similarly unassailable if all goes well Sunday afternoon.

The NFL season is always an unpredictable march, but the Cardinals' inordinately high number of roadblocks continued to pile up this week. Linebacker John Abraham (concussion) was placed on season-ending injury reserve, running back Jonathan Dwyer was deactivated after getting charged with domestic violence, and backup quarterback Drew Stanton was anointed Sunday's starter as Carson Palmer still deals with a shoulder injury.

It's the latest round of adversity, added to linebacker Karlos Dansby's departure in free agency, linebacker Daryl Washington's

season-long suspension, defensive tackle Darnell Dockett's season-ending knee injury and other issues.

And yet, the Cardinals won with Stanton on the road last week in New York, and enter their showdown with the 49ers at 2-0 and in sole possession of first place in the rugged NFC West. The start reminded Arians of the 2010 season when he was the offensive coordinator in Pittsburgh, where the Steelers cycled down to fourth-string quarterback Charlie Batch within the first four games, but still went 3-1 and eventually made the Super Bowl.

No matter the issue, Arians fervently believes his team must find a way to overcome it.

"It's something we've been through and it's what you hold each other accountable to," Arians said. "It's not lip service looking for excuses. There are no excuses."

The Cardinals are not yet seen as the 49ers or Seahawks' equal, but a home win would put them two games ahead of San Francisco early in the year and at least one game ahead of Seattle, which hosts the Broncos in a Super Bowl rematch on Sunday. There's plenty that can change as the season wears on, but it would be a nice cushion.

"What happens in December is what's really going to matter, but we've set ourselves up," Arians said. "If we can pull this one out, December might be a little more important."

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Since the format expanded to a 12-team playoff structure in 1990, three-quarters of teams who started 3-0 have made the playoffs. Those who began 2-1 have qualified 53 percent of the time. Stacking up wins now seems especially imperative for the Cardinals, who face one of the league's toughest schedules the rest of the way, including road games at the 49ers, Seahawks and Broncos.

"This game is early, but it means a lot," cornerback Patrick Peterson said.

The Cardinals look much different than expected, but so do the 49ers. San Francisco will be without star linebackers Aldon Smith (suspension) and NaVorro Bowman (knee) as well as defensive tackle Glenn Dorsey (biceps). Additionally, standout tight end Vernon Davis – who plays a position which has given the Cardinals trouble under Arians – is questionable for the game with an ankle injury and didn't practice all week.

The 49ers have a revamped secondary, which allowed four passing touchdowns in last week's 28-20 loss to the Bears, and may be without the services of starting cornerback Tramaine Brock (toe).

When these teams meet again the season finale, Bowman and Smith should be back, and that matchup could have a distinctly different feel. While both squads will take the field short-handed in this one, the outcome is of equal importance.

"I think any time you play a divisional game, it's a big game and you want to win," 49ers wide receiver Anquan Boldin said.

As the Cardinals know, even a 3-0 start would not guarantee a path to the postseason. They won their first four games in 2012 before dropping nine in a row and finishing 5-11. This group, though, figures to have more staying power.  The team has won 9 of its past 11 games dating back to the middle of last season, outdone by only one-loss Carolina in that stretch.

While the Cardinals are undefeated this year, it has taken two fourth-quarter comebacks against the Chargers and Giants to get there. The 49ers are among the NFC elite and have won nine of the past 10 games in this series, so it could be a lucid measuring stick.

"If we want to be the team we know we're capable of being, this is a game that has to be won," wide receiver Larry Fitzgerald said. "No ifs, ands or buts about it."